Sorbic acid and/or its derivatives, such as potassium sorbate, as a preventative for rust, corrosion and scale on metal surfaces

ABSTRACT

An aqueous solution that will prevent rust, corrosion and scale on metal surfaces that includes potassium sorbate at percentages above 0.3%. This aqueous solution is effective at pH 4.5. However, its optimum effectiveness as a rust preventive is at pH 6.0 and above. The solution can be produced in a concentrated form and then diluted with tap or deionized water. The potassium sorbate solution has reduced conductivity and reduced oxygen content, both relative to tap water. This is believed to be the technical basis for its ability to prevent rust. Furthermore, the combination of lower conductivity and reduced oxygen content renders the potassium sorbate solution less viable for microbiological growth which prevents the solution from becoming rancid when it is used in re-circulating water systems. This also permits the use of toxic biocides to be eliminated in re-circulatory water systems, which are often used to reduce and control microbiological growth. Also, the solution can be substituted for tap water in water-based products, such as paints, which eliminates the need to plate the cans.

FIELD OF THE INVENTION

The invention relates to sorbic acid and its derivative potassiumsorbate for use as a preventative against rust, corrosion and scale thatusually forms on metal surfaces.

BACKGROUND OF THE INVENTION

Sorbic acid and its salts are commonly used to preserve foods such ascheese, fish, meat, vegetables, fruit, non-alcoholic beverages, wine,confectioneries and baked goods. Sorbic acid and its salts are also usedas preservatives in some pharmaceuticals and cosmetics. Potassiumsorbate (hereinafter PS) or 2,4 hexadienoic acid potassium salt, isextensively used as a wide spectrum anti-microbial for maintainingfreshness in foods, beverages, animal feed, cosmetics and as apreservative for products destined to come in contact with foodstuffssuch as adhesives for food packaging. PS has excellent water solubilityas compared to sorbic acid which has low water solubility. PS is highlyeffective against most micro-organisms, is economical and has obtainedworldwide approval for use in a wide variety of foods. The concentrationof sorbic acid and its salts as a preservative, in food in which thepreservative is evenly dispersed, is about 0.1% and generally falls inthe range of 0.05% to 0.3%. Some food products are dipped or sprayedwith a PS solution that has a concentration of 5-10%, however, theconcentration of the preservative in these final products fall withinthe above range.

The effectiveness of all food preservatives is highly dependent upon thepH of the preservative. The optimum effectiveness of PS as a foodpreservative is when it is used below pH 6.0. However, it is aneffective food preservative at up to pH 6.5 which qualifies PS to beused in a very wide variety of foods.

The major manufacturer of potassium sorbate in the United States isEastman Chemical in Kingsport, Tenn. The largest manufacturer of PS isHoechst Celanese of Frankfurt, Germany. There are a limited number oflarge manufacturers of PS in the world, one being in Japan and anotherin Denmark.

Although sorbic acid and its salts have been found to be effectiveagainst a long list of microorganisms that are responsible for fooddecay, its use as a rust preventative agent has not been previouslyrecognized. There is currently no known published literature thatdiscloses the use of PS for other than its widespread anti-microbialuse, primarily in products directly or indirectly related to food, withsome acknowledgement of its anti-microbial effect in unrelated foodproducts, such as cleaning solutions primarily used for cleaning areasinvolving food, such as food preparation or processing areas.

Corrosion is a very serious problem in many industries. According to anarticle in McGraw Hill Encyclopedia of Science & Technology, “The costof corrosion in the United States and other industrial countries hasbeen estimated to be on the order of 4% of the gross national product.”This estimated cost includes both the replacement cost and the cost ofprotecting against corrosion. Extensive efforts have been made in thedesign of products such as steam generators, heat exchangers, bridges,oil platforms and motor vehicles to minimize the destructive effects ofcorrosion. However, corrosion remains a problem in these traditionalproducts. In addition to traditional products, new developments in theareas of energy sources, new materials and microprocessors present newchallenges in the fight against corrosion. As new devices are developedon a submicrometer scale, even smaller amounts of corrosion will resultin device failure.

For these reasons, a new method and product that is effective to preventand guard against corrosion of metal is needed.

BRIEF SUMMARY OF THE INVENTION

It is the object of the invention to provide an aqueous solution thatwill prevent rust. The aqueous solution of this invention includes PS inthe form of powder or granules that have been dissolved in ordinary tapwater or deionized water, at percentages above 0.3%. PS is at itsoptimum effectiveness as a rust preventive at pH 6.0 and above.

The formula for producing applicant's PS solution rust inhibitor, in aconcentrated form, is to mix at the following ratio 269.5 ml of water(49.9%). 0.5 ml of sodium nitrate (0.1%) and 270.0 ml of potassiumsorbate (50.0%). This concentrated rust inhibitor will have a pH ofabout 10.2. One part of the concentrate should be diluted with 16 partstap water or deionized water to produce applicant's rust preventivewater. This diluted rust preventive water will have about a pH of 6.5.

The PS dosages for rust and corrosion prevention differ from the dosagesof PS that are used for the prevention of microbial degradation. PSconcentrations are effective as anti-microbial food preservatives,generally in the range of 0.05% to 0.3%. Higher dosages are not usedbecause of the bitter taste that is imparted by PS.

The low concentration of PS currently used in the food industry are noteffective for preventing rust, corrosion and/or scale. Concentrations ofPS above 0.3% in aqueous systems have been found to be increasinglyeffective against the rusting, corroding or scaling of metal with afail-safe concentration of ±1.75% laboratory tested as consistently andindefinitely preventing rust, corrosion and/or scale.

Applicant has found that the PS solution of this invention has reducedconductivity and reduced oxygen content of tap water and believes thatthis is the technical explanation of how applicant's PS solutionfunctions to prevent rust. Furthermore, the combination of lowerconductivity and reduced oxygen content renders the PS solution lessviable for microbiological growth. This feature of applicant's PSsolution is responsible for eliminating rancidity in re-circulatingwater systems due to mold. Toxic biocides are often added tore-circulatory water systems to reduce and control microbiologicalgrowth. The elimination or reduction of biocides in re-circulatory watersystems is an added enhancement of this invention. Furthermore, bysubstituting the PS solution for tap water in water-based products, suchas paints, will also eliminate or reduce the addition of toxic biocides.

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request and payment of the necessaryfee.

FIG. 1 is an enlarged black and white photograph of a production steelbar that has been exposed to tap water for 7 days.

FIG. 2 is a further enlarged black and white photograph of a section ofthe steel bar seen in FIG. 1.

FIG. 3 is an enlarged black and white photograph of a production steelbar that has been exposed to applicant's non rust PS solution for 7days.

FIG. 4 is a further enlarged black and white photograph of a section ofthe steel bar seen in FIG. 3.

FIG. 5 shows the EDS spectra for the heavy corrosion area of FIG. 1.

FIG. 6 shows the EDS spectra for the area shown in FIG. 2 where the rusthad fallen and the surfaces were pitted.

FIG. 7 shows the EDS spectra for the test bar shown in FIGS. 3 and 4.

FIG. 8 shows the EDS spectra for a sample test bar that had not beenexposed to the corrosion test.

FIG. 9 is a color photograph of the test samples and containers of thetest solution prior to the start of an Immersion Corrosion Test.

FIG. 10 is a color photograph of the test samples in the test solutionsat the beginning of the Immersion Corrosion Test.

FIG. 11 is a side view color photograph of the test samples in the testsolution taken 24 hours after the beginning of the test.

FIG. 12 is a top view color photograph of the test samples in the testsolution taken 24 hours after the beginning of the test.

FIG. 13 is a side view color photograph of the test samples in the testsolution taken 72 hours after the beginning of the test.

FIG. 14 is a top view color photograph of the test samples in the testsolution taken 72 hours after the beginning of the test.

FIG. 15 is a side view color photograph of the test samples in the testsolution taken 7 days after the beginning of the test.

FIG. 16 is a top view color photograph of the test samples in the testsolution taken 7 days after the beginning of the test.

FIG. 17 is a color photograph of the test samples after being removedfrom the Immersion Corrosion Test after the 7-day exposure.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with this invention, when PS in the form of powder orgranules is dissolved in ordinary tap or deionized water at percentagesabove 0.3%, this PS aqueous solution will prevent rust, corrosion andscale on metal surfaces.

A visual demonstration of this invention can be produced by immersing anun-galvanized nail in a container of tap water and a similarun-galvanized nail in a container of the PS solution of this invention.The nail in the tap water will begin rusting within hours. However, thenail in the PS solution of this invention will show no signs of rusting.

Another visual demonstration of this invention can be produced byfilling a first steel can with tap water and a second steel can with thePS solution of this invention. The inside of the steel can containingtap water will rust rapidly while the other can containing the PSsolution of this invention will not rust and will have an unlimitedshelf life against rust.

The non-rusting technology of this invention is of great value tomanufacturers of water-based products (such as latex paints), as well asthe can manufacturers that produce the container for such water-basedproducts. Currently, steel cans made for water-based products arecoated, at great expense, to prevent rust.

By substituting the non-rusting PS water solution for the tap water ordeionized water now used in the manufacturing of water-based products,the can manufacturer can reduce the expensive coating costs of theirproducts currently used to prevent rust.

Any other water-based product that is packaged in steel cans can use thePS solution and will benefit from similar cost reductions as a result ofthis PS water solution technology.

Another important use for the PS solution of this invention is inre-circulating water systems. Re-circulating water systems experiencevarious degrees of rust and/or scale. Expensive chemical corrosioninhibitors are added to inhibit this rusting and/or scaling.Re-circulating water systems of the type referred to include, but arenot limited to, boilers, cooling towers, heat exchangers, condensers,injection molding machines, etc. Rust, corrosion and scale in all suchwater re-circulatory systems is prevented when the PS water technologyof this invention are used.

The list of industrial, agricultural, commercial and household equipmentthat experiences rust caused by aqueous solutions is enormous. TheMcGraw-Hill Encyclopedia of Science and Technology states that the cost,in the United States and other industrial countries, of replacing andprotecting equipment against corrosion represents about 4% of the grossnational product.

Numerous consumer products can be protected from rust and corrosion bymerely immersing and storing them in the PS solution of this invention.Examples of such steel products that currently suffer from rust arerazor blades, and fish hooks and lures.

The PS dosages for rust and corrosion prevention differ from the dosagesof PS that are used for the prevention of microbial degradation. PSconcentrations are effective as anti-microbial food preservatives,generally in the range of 0.05% to 0.3%. Higher dosages are not usedbecause of the bitter taste that is imparted by PS.

The low concentration of PS currently used in the food industry is noteffective for preventing rust, corrosion and/or scale. Concentrations ofPS above 0.3% in aqueous systems have been found to be increasinglyeffective against the rusting, corroding or scaling of metal with afail-safe concentration of ±1.75% laboratory tested as consistently andindefinitely preventing rust, corrosion and/or scale.

Samples of the PS solutions of this invention have been subjected to acontinuous lab test by the inventor, as well as being tested by outsidetesting laboratories. In the outside lab test, 2 ounces of PS, in powderor granular form, was dissolved in one gallon of tap water. The PS willdissolve rapidly in cold or hot tap water or deionized water. Theresulting PS solution has a pH in the range of 6.5 to 8.0. The pH of thePS solution depends upon initial pH of the tap or deionized water.

Lowering of the pH of the PS solution, for a particular application, canbe achieved by the addition of citric acid. Provided the pH of the PSsolution is maintained above 4.5, the non-rusting effectiveness of thePS solution does not significantly change.

Applicant has established through testing that the PS solution of thisinvention has reduced conductivity and reduced oxygen content bothrelative to tap water. It is applicant's opinion that this is thetechnical explanation for the resulting rust prevention. This conclusionis based upon the following test results: Tap Water 1.75% PS WaterSpecific Conductivity 344 umhos/cm 13,500 umhos/cm at 25% c DissolvedOxygen  9.3 mg/l   7.5 mg/lApplicant is not aware of any published literature disclosing thisreduction in conductivity and oxygen content at this concentration ofPS. 8

When steel products such as rods, sheets and structural beams areproduced at a steel mill, an oil coating is applied to prevent rustduring shipping. However, this coating soon loses its effectiveness andthe products become vulnerable to rust. Also, if the steel products areto be painted or coated in their final use, the oil coating must becompletely removed to insure that the paint or coating properly adheres.A serious disadvantage of the protective oil coating is that itcontaminates everything that the product comes into contact with. Steelproducts such as rods, sheets and structural beams can be dipped in orsprayed with applicant's PS solution, and they will not have thedisadvantage of contaminating everything that they come into contactwith and could be painted or coated without removing the protectivecoating.

In the test results that are shown in FIGS. 1-4, the steel bars had noprotective oil coating before the test began. In this test, plain carbonsteel rods, having a diameter of 0.137 inches and 1.75 inches in length,were used. The surfaces of the steel rods were lightly ground andultrasonically pre-cleaned in ethyl alcohol to remove any organiccoatings, dirt debris or inherent oxide films which might interfere withthe corrosion test. Some rods were placed in clean glass beakers andcovered with plain untreated tap water. Other rods were placed in cleanglass beakers and covered with applicant's PS solution. The steelsamples and liquid media were maintained at approximately 70° F. for theduration of the test. The test was monitored on a daily basis to ensurethat the steel samples maintained a nominal temperature of 70° F. Thecondition of the samples was noted after 24 hours, 72 hours and at theend of the test period. The procedures and test methods were generallyperformed in accordance with ASTM Standard G31-72 (1995): “StandardPractice for laboratory Immersion Corrosion Testing of Metals.”

At the beginning of the test, the surfaces of all the samples were cleanand metallic in appearance. After 24 hours, there was a strikingdifference between the test samples. The samples that were in tap waterwere already severely corroded. However, the samples that were in the PSsolution still had a clean, shiny metallic appearance. After 72 hours,the differences between the two samples were more pronounced. The testwas completed after 7 days. At the end of the test, the samples that hadbeen in tap water were extensively corroded, while the samples that hadbeen in the PS solution still had a clean shine metallic appearance.FIGS. 1-8 illustrate results from this test.

FIG. 1 is an enlarged photograph of the surface of a sample steel barthat has been exposed to tap water for 7 days. There is extensivecorrosion present over the surface of the bar.

FIG. 2 is a photograph of a section of the steel bar seen in FIG. 1 thathas been further enlarged. A block has been drawn in FIG. 1 indicatingthe area of FIG. 2. In the area of FIG. 2, the rust had fallen off. Theremaining surface is rough and pitted.

FIG. 3 is an enlarged photograph of the surface of a sample steel barthat has been exposed to applicant's non rust PS solution for 7 days.The enlargement of this photograph corresponds to the enlargement ofFIG. 1. There is no corrosion present over the surface of the bar.

FIG. 4 is a further enlarged photograph of a section of the steel barseen in FIG. 3. The enlargement of this photograph corresponds to theenlargement of FIG. 2. Even at this degree of enlargement, there is nocorrosion visible on the surface of the bar.

An Energy Dispersive Spectrography (EDS) analysis on the surfaces ofsamples from both test groups and on the surface of clean, untestedsteel sample was performed.

FIG. 5 shows the EDS spectra for the heavy corrosion area of FIG. 1 andindicates that it is predominantly iron and oxygen, i.e. iron oxide.

FIG. 6 shows the EDS spectra for the area shown in FIG. 2 where the rusthad fallen off and the surfaces was pitted. Although this area is lessoxidized, there is still a significant amount of oxygen presentsuggesting that the surface was corrosively attacked.

FIG. 7 shows the EDS spectra for the test bar shown in FIGS. 3 and 4.This bar had been exposed to applicant's PS solution for 7 days. Onlyiron, manganese, silicon and carbon were detected on the surface of thissample, which are the common elements expected to be found in alow-carbon steel. No oxygen, nitrogen or other elements indicative ofsurface corrosion were found on the surface of this test sample.

FIG. 8 shows the EDS spectra for a sample bar that had not been exposedto the corrosion test. This test was performed for comparative purposes.Other than a slight amount of aluminum present on this surface, it isidentical to the steel bar sample which had been exposed to the PSsolution and shown in FIG. 7. The aluminum on the surface of this sampleis probably a residue from the grinding paper used to clean its surfacebefore examination.

FIGS. 9-17 are color photographs of a test that was conducted over aseven-day period. This test is similar to the test that is shown anddiscussed with reference to FIGS. 1-8. However, in each of FIGS. 9-17,the test specimens and the liquid that they are being exposed to areshown side-by-side. The rust on the specimens that are being exposed tothe tap water becomes very apparent as the test progresses. The rust isnot only visible on the specimens, but also in the tap water whichbecomes discolored by the rust.

FIG. 9 is a color photograph of the test specimens prior to beingexposed to the liquid. The test specimens are un-galvanized nails. Theleft beaker contains tap water and the right beaker contains applicant'sPS solution which is labeled “Rustproofer”™, which is the trademark thatapplicant is contemplating using for his PS solution. In this Figure,all test specimens are clean and metallic in appearance and the liquidsare clear and have no discoloration.

FIG. 10 is a color photograph of the test specimens in the liquids. Thiscolor photograph was taken immediately after the specimens were placedin the beakers containing the liquids. In this Figure, all testspecimens are clean and metallic in appearance and the liquids are clearwith no discoloration.

FIG. 11 is a front view color photograph of the test specimens in theliquids taken 24 hours after the test was started. In this Figure, thetap water in the beaker to the left shows some discoloration and thetest specimens in this beaker show some evidence of rust. In thisFigure, the PS solution in the beaker to the right is clear with nodiscoloration and the test specimens in this beaker remain clean andmetallic in appearance.

FIG. 12 is a top view color photograph of the test specimens in theliquids taken 24 hours after the test was started. In this Figure, thetap water in the beaker to the left shows some discoloration and thetest specimens in this beaker show some evidence of rust. In thisFigure, the PS solution in the beaker to the right is clear with nodiscoloration and the test specimens in this beaker remain clean andmetallic in appearance.

FIG. 13 is a front view color photograph of the test specimens in theliquids taken 72 hours after the test was started. In this Figure, thetap water in the beaker to the left clearly shows discoloration and thetest specimens in this beaker show some evidence of rust. In thisFigure, the PS solution in the beaker to the right is clear with nodiscoloration and the test specimens in this beaker remain clean andmetallic in appearance.

FIG. 14 is a top view color photograph of the test specimens in theliquids taken 72 hours after the test was started. In this Figure, thetap water in the beaker to the left clearly shows discoloration and thetest specimens in this beaker show some evidence of rust. In thisFigure, the PS solution in the beaker to the right is clear with nodiscoloration and the test specimens in this beaker remain clean andmetallic in appearance.

FIG. 15 is a front view color photograph of the test specimens in theliquids taken 7 days after the test was started. In this Figure, the tapwater in the beaker to the left is discolored and the test specimens inthis beaker clearly show evidence of rust. In this Figure, the PSsolution in the beaker to the right is clear with no discoloration andthe test specimens in this beaker remain clean and metallic inappearance.

FIG. 16 is a top view color photograph of the test specimens in theliquids taken 7 days after the test was started. In this Figure, the tapwater in the beaker to the left shows discoloration and a circle of rustresidue can be seen on the bottom of the beaker. The test specimens inthis beaker clearly show evidence of rust. In this Figure, the PSsolution in the beaker to the right is clear with no discoloration andthe test specimens in this beaker remain clean and metallic inappearance.

FIG. 17 is a perspective view color photograph of the test specimensafter having been removed from the beakers at the end of the test. Thespecimens that were in the tap water are on the left side and thespecimens that were in the PS solution are on the right side. In thisFigure, the specimens that were exposed to tap water have rust on theirsurfaces and the specimens that were exposed to the PS solution have norust. If the specimens on the right in FIG. 17 are compared to thespecimens before the test commenced, as seen in FIG. 9, there has beenno visible deterioration of the specimens as a result of being exposedto the PS solution for 7 days. After 7 days of exposure to the PSsolution, the specimens are clean and metallic in appearance.

The foregoing specification describes only preferred embodiments of theinvention as shown. Other embodiments may be articulated as well. Theterms and expressions, therefore, serve only to describe the inventionby example only and not to limit the invention. It is expected thatothers perceive differences which, while differing from the foregoing,do not depart from the spirit and scope of the invention hereindescribed and claimed.

1. An aqueous solution that prevents the formation of rust, corrosion and scale on metal surfaces that are exposed to it comprising: potassium sorbate dissolved in tap water or deionized water at a concentration of 0.3 %, by weight, or higher, the aqueous solution having a pH of 4.5 or higher.
 2. The aqueous solution as set forth in claim 1 in which the concentration of potassium sorbate is in the range of 0.30% to 1.75%.
 3. A concentrated form of aqueous solution that, when diluted with 16 parts of tap water or deionized water, prevents the formation of rust, corrosion and scale on metal surfaces that is exposed to it comprising a solution formed in accordance with the following ratio of ingredients: 269.5 milligrams of tap or deionized water; 0.5 milligrams of sodium nitrate; and 270.0 milligrams of potassium sorbate.
 4. The method of producing a concentrated form of aqueous solution for use as a rust preventor comprising the steps of: a) providing 269.5 milligrams of tap or deionized water to a mixing container; b) adding 0.5 milligrams of sodium nitrate to the mixing container; c) adding 270.0 milligrams of potassium sorbate to the mixing container; and d) mixing the contents of the mixing container.
 5. The method of producing a aqueous solution for use as a rust preventor comprising the steps of: a) providing a multiple of 269.5 milligrams of tap or deionized water to a mixing container; b) adding 0.5 milligrams, multiplied by the same multiple, of sodium nitrate to the mixing container; c) adding 270.0 milligrams, multiplied by the same multiple, of potassium sorbate to the mixing container; and d) diluting the contents of the mixing container with 16 parts of tap or deionized water. 